As more and more composers, musicians and producers discover the benefits of monetising their creative endeavours with sync and/or production libraries (if you don't do this, you should!), the need to stand out in an ever-expanding and competitive industry is evermore important. Peruse the contents of many libraries and you will hear that the quality of audio is not always that great. The reason is that if you've spent x number of years learning how to play and compose music, then mixing and mastering is often an afterthought and you may not fully understand why your mixes are not sounding so great. Using A.I. driven mastering solutions is a quick and cheap way of getting perceived improvement but ultimately, if you want to stand out and have your music used many times (and earn decent royalties from them) the audio needs to sound good. To become really successful, it needs to sound great!
So spending time learning how to mix for professional release is vitally important. Spending time learning how to master is another topic for another blog post, but I will say this: Some libraries only accept 'mastered' audio, while others don't accept mastered audio because they use the services of professional mastering engineers (with professional studios, equipment and years of experience) to get the best results for a given piece of audio. Those libraries invest time, effort and money in getting your tracks sounding as good as possible in order to get more use out of them, earning you (and them) more income. Those libraries that only accept mastered audio...well, go peruse, you'll probably hear the difference.
Now obviously I'm biased, but I do a lot of work for some of the best libraries around and my job in this field is really hard because the mixes I receive are predominantly bad. Work I get from professional producers and record labels is great because the mixes are great (often having been mixed by a professional mix engineer) meaning the masters will sound great. Mixes that sound good when they get to me always sound great after mastering and those are the tracks that will succeed amongst the sheer volume of (what I will arguably call) sub-standard content. I don't mean the compositions, 99% of those are great! I mean the mixes.
The summary of this post is this: if you plan on making your money in library or with sync then invest in 2 things.
Time in watching mixing tutorials on youtube if you're short on money or sign up to a mixing course at your local music college. It doesn't matter how old you are. If you're straight out of school but can bake beats with Albelton or a 40 year old musician entering the world of library for the first time, you NEED to understand how to eq (and compress if needed) each individual track in your project so as to leave space within the frequency spectrum for the other tracks in your mix. Many samples for example have masses of needless sub in them that can be eq-ed out completely freeing up MUCH needed space in the low end for bass instruments for example.
Room Correction Software (like Sonarworks, or a Trinnov system if you're feeling really flush!). Bedrooms and non-professional studio spaces alter the sound coming from your speakers, so when it hits your ears, it's altered. You then make mix decisions based on a sound that is influenced by your room, not by the audio itself. N.B. Some basic acoustic sound absorbtion or diffusion at the 1st reflection points (ceiling and walls that reflect direct sound from your speakers) and corner traps are highly recommended for Sonarworks to work best, but it then sweeps the entire frequency range from bottom to top with a sine wave to determine how your room is affecting the sound coming from your speakers. It then alters the output to take into account those alterations, giving you a more accurate representation of your audio with which to work.
I can't over-emphasise enough how important these two things are. If you're serious about your music and you want to build a successful music portfolio that will potentially pay you for many years (or even decades) to come while soundly asleep in your bed, then you need to sort out your mixing skills and your listening environment.